This invention relates to a pilot operated check valve for high pressure service utilizing an O-ring form of seal.
When pilot operated check valves are employed in circuits where the difference in fluid pressure between the outlet side and the inlet side is insubstantial or in check valves which have not pilot operation means, an O-ring is commonly used in the valve seat or the seating surface of the poppet valve to provide an oil seal between the valve seat and the poppet valve. However, no known pilot operated check valves utilize an O-ring for this oil seal when a substantial pressure difference such as 70 or 100 atm. P. exists between the outlet side and the inlet side. The reason is that where the pressure on the outlet side is extremely high relative to the pressure on the inlet side and the poppet valve is piloted toward the open position by mechanical or hydraulic means, the O-ring which has been functioning as a seal between the poppet valve and the valve seat is instantly forced out of the ring groove as the clearance between the poppet valve and the valve seat exceeds the threshold extrusion clearance limit (which is determined by the hardness of the O-ring used and the level of hydraulic pressure).
The pilot operated check valves for high pressure service known heretofore are of metal fit type. This type has a disadvantage in that no sufficient sealing is provided, with the result that oil leakage occurs in the course of time. As an approach to eliminate such oil leakage, there is a pilot operated check valve design of metal fit type in which the poppet valve and the valve seat are respectively constructed of metals having different degrees of hardness so that pressure sufficient to bring one of the metals to its yield point may be acted upon the poppet valve in the presence of a difference in pressure between the primary side and the secondary side.
Previous attempts have been made to provide a pilot operated check valve in which an O-ring serves as a perfect oil seal and will not be forced out of the ring groove during valve opening operation even where the difference in pressure between the inlet side and the outlet side is substantial. The present inventor previously proposed a pilot operated check valve comprising a spool 15' formed integrally with a poppet valve 3' on the front side thereof and projecting axially therefrom, as shown in FIG. 1, a fluid flow groove 16' provided on the spool 15' and extending from the front end thereof to a surface position adjacent the rear end thereof, an O-ring mounting groove 19' formed on a seating surface 3'a of the poppet valve 3' adapted for engagement with a valve seat 17'a, an O-ring 20' mounted in the O-ring mounting groove 19', the spool 15' being slidably and closely fitted into a fluid passageway 18' extending through a partition wall 17' defining the valve seat 17'a (Japanese Patent Publication No. 45009/1978, dated Dec. 4, 1978). In this pilot operated valve, as seen from FIG. 2 showing a key portion thereof in section, the O-ring mounting groove 19' is formed on the seating surface 3'a of the poppet valve 3' opposed to the valve seat 17'a. The O-ring 20' mounted in the groove 19' is squeezed against the surface of the valve seat 17'a when the seating surface 3'a is forced into engagement with the valve seat 17'a. As such, the O-ring mounting groove 19' is formed in shallow relation with the peripheral surface 15'a of the spool 15' and accordingly the O-ring 20' protrudes substantially beyond the peripheral surface 15'a of the spool 15'. However, it has been found that the pilot operated check valve as shown in FIGS. 1 and 2 still involves the following difficulties. When the poppet valve 3' is piloted to the open position against the high-level hydraulic pressure on the secondary side, the O-ring 20' is subject to a substantial shear force due to the secondary-side hydraulic pressure acting on that portion of the O-ring 20' which protrudes outwardly beyond the peripheral surface 15'a of the spool 15' to force it against the valve seat 17'a. The O-ring is also subject to the pilot pressure acting along a circumferential edge 19'a of the spool 15' abutting the O-ring mounting groove 19' to force it against the secondary-side hydraulic pressure. Another difficulty is that if no pressure or a very low pressure is present on the secondary-side, it is impracticable to permit the outer periphery of the O-ring 20' to get squeezed against the valve seat 17'a to the extent that the O-ring is deformed in section under the force of the spring 21' only. Such deformation is likely to lead to oil leakage in the course of time.
It is a primary object of this invention to provide a pilot operated check valve having improved features over the above said design and which eliminates the above mentioned difficulties and better facilitates pilot operation. The improvement includes a spool member formed integrally with and projecting axially from the front side of a poppet valve having a seating surface for engagement with a valve seat. An O-ring mounting groove is provided on the spool member in abutment relation with the front side of the poppet valve, and a passage or opening for fluid flow is provided in the spool member. The passage or opening connects a fluid compartment on the primary side and a surface of the spool member adjacent the O-ring mounting groove. An O-ring is mounted is the O-ring mounting groove. The spool member is slidably and closely fitted in a fluid passageway which extends through a partition wall defining the valve seat so as to permit the O-ring to be positioned in the fluid passageway upon the seating surface of the poppet valve being brought into engagement with the valve seat. The improvement further comprises a small groove or hole bored and extending through the poppet valve or through the partition wall for communication between the secondary side of the O-ring mounting groove sealed by the O-ring and a secondary-side fluid compartment separated from the primary-side fluid compartment by the partition wall. In addition, the corner edge of the secondary-side end of the fluid passageway is flared so as to provide a curved surface for guiding the O-ring into the fluid passageway.
Other features, objects and advantages of this invention will become apparent from the following detailed description of embodiments with reference to the accompanying drawing.